Metal compound films, such as metal oxynitrides, metal oxycarbides, metal carbon nitrides, metal silicide nitrides, etc., have a range of composition in which the properties of films vary. For typical semiconductor applications, it is necessary to control the range of the film composition within a specification window around a target.
One such application is a stack of a metal gate layer and a high-k dielectric layer, which is subjected to high temperature processing steps after deposition. The metal of choice is often a metal compound that can withstand the high temperature processing steps, for example, source and drain activation anneals. Depending on the composition of the metal compound, however, the high temperature anneal may affect the underlying silicon oxide interfacial layer or other features of the stack in different manners. For example, a TiN composition with a high atomic percent of Ti can scavenge the oxygen in the interfacial layer. If too much oxygen is gettered by the TiN during deposition, however, an interfacial layer regrowth may occur. Deviation of the composition from a desired target may result in adverse effects in device performance such as degraded mobility and threshold voltages in a semiconductor device.
Thus, in-line monitoring of composition of the metal compound film is necessary to insure that device performance is controlled within a target range. Typical analytical methods for monitoring the composition of a metal compound film include sheet resistance measurement, secondary ion mass spectroscopy (SIMS), Auger spectroscopy, etc. While the resistance measurement is effective in monitoring the film composition of a limited number of metal compounds, the resistance of many other metal compounds is not sufficiently sensitive to the composition. Further, the resistivity of the metal compound needs to be deconvoluted from the resistance measurement by a separate measurement of the thickness of the metal compound film. In the case of other destructive measurement methods such as SIMS or Auger spectroscopy, the measurement typically involves extensive manual intervention as well as destruction of a wafer, oftentimes in an ex-situ environment.
Therefore, there exists a need for a non-destructive in-line monitoring method to determine the composition of a metal compound film.
Further, there exists a need for a method of controlling the composition of a metal compound film that employs an effective and accurate in-line measurement of the film composition.